Desert Southwest getting flooded by Rosa

Tropical Storm Rosa is still hours away making landfall in Baja California, but parts of the Desert Southwest have already been drenched by the storm’s rains.

Yuma, Arizona has already received more than half its average yearly rainfall because of Rosa. Deep tropical moisture associated with the system dropped around two inches of rain there on Sunday. Andrew Deemer, a meteorologist at the National Weather Service in Phoenix, says flooding has already been reported in Yuma and some areas south of Phoenix.

The Imperial Airport in El Centro, California reported around three quarters of an inch of rain on Sunday. According to Deemer there isn’t an official climate record for El Centro, but the data he has for a few other nearby locations show an average annual rainfall of just two to three inches.

This part of the country gets rain from tropical systems every few years, but has been in an “Extreme Drought” for several months. Prolonged rain and heavy downpours can lead to flooding here regardless of soil moisture content. Flooding can lead to rock slides and mudslides which Deemer says have happened “from time to time”. But there’s a silver lining beyond the immediate negative impacts: the rain will replenish reservoirs and help grass and shrubs grow in forests and on ranch lands.

Flash flooding will be an ongoing threat through at least Tuesday night, and a Flash Flood Watch is in effect for the region until early Wednesday morning. The focus for most of the rain and flood threat from here on out will shift to the Phoenix metro area where the forecast is for two to three inches, with higher amounts possible in the mountains to the north. However, Demer says Yuma and El Centro could get more rain, too, and after Rosa leaves there could be even more rain coming to the region later in the week as a low pressure system approaches the west coast.

The latest report from the National Hurricane Center has Rosa making landfall on the central part of Baja’s west coast tonight, moving into the Desert Southwest on Tuesday a tropical depression with weaker winds.